1. Field of the Invention
The present invention relates to a thin film transistor using a Metal Induced Crystallization (MIC) process and method for fabricating the same, and an active matrix flat panel display using the thin film transistor. More particularly, the invention relates to a thin film transistor using a Metal Induced Crystallization (MIC) process and method for fabricating the same. The invention also relates to an active matrix flat panel display using the thin film transistor, which is formed by the method including forming a crystallization inducing metal layer beneath a buffer layer to diffuse the crystallization inducing metal layer.
2. Description of the Related Art
A method for forming a polycrystalline silicon layer used for the active layer of the thin film transistor comprises depositing an amorphous silicon layer on an insulating substrate, and then performing crystallization at a predetermined temperature.
Solid Phase Crystallization (SPC) by means of thermal treatment, Eximer Laser Annealing (ELA) by means of laser crystallization and Metal Induced Crystallization (MIC), or the like may be employed to crystallize the amorphous silicon layer.
However, the SPC method requires a high temperature for the crystallization and a long time for the process, and the ELA method has the following problems: high-priced equipment investment, temporal and spatial unevenness caused by laser instability, and striped defects due to the laser.
On the other hand, the MIC method has an advantage in that the conventional thermal treatment equipment may be employed, but only a relatively low processing temperature and short time is required for processing.
FIGS. 1A, 1B, 1C, and 1D show cross-sectional views of the process for explaining a method for fabricating a thin film transistor using the conventional metal induced crystallization method.
As shown in FIG. 1A, an amorphous silicon layer 120 may be formed on an insulating substrate 100 having a buffer layer 110, and a crystallization inducing metal layer 130 may be formed on the amorphous silicon layer 120 to perform the MIC process.
As shown in FIG. 1B, the insulating substrate 100 on which the crystallization inducing metal layer 130 is already formed may be subject to thermal treatment in a furnace to crystallize the amorphous silicon layer 120 into a polycrystalline silicon layer 123.
As shown in FIG. 1C, after the crystallization inducing metal layer 130 is removed, the polycrystalline silicon layer 123 may be patterned to form an active layer 125 primarily consisting of polycrystalline silicon.
As shown in FIG. 1D, after the active layer 125 is formed, a gate insulating layer 140 and gate electrode material may be formed on the insulating substrate 100, and the gate electrode material may be patterned to form a gate electrode 150.
After the gate electrode 150 is formed, predetermined impurities may be implanted using the gate electrode 150 as a mask to form source/drain regions 125S and 125D in the active layer 125. In this case, a region between the source/drain regions 125S and 125D may act as a channel region 125C.
After the source/drain regions 125S and 125D are formed, an interlayer insulating layer 160 may be formed on the entire surface of insulating substrate 100 having the gate electrode 150 to have contact holes 161 and 165 for exposing some portions of the source/drain regions 125S and 125D.
After the interlayer insulating layer 160 is formed, source/drain electrodes 171 and 175 electrically connected to the source/drain regions 125S and 125D may be formed through contact holes 161 and 165 to form a thin film transistor.
However, in the thin film transistor fabricated by the above-mentioned process, the thin film transistor may be directly contacted with the crystallization inducing metal to be crystallized when the MIC process is performed, which may cause the crystallization inducing metal to be diffused into the active layer and to be residual.
In this case, when the amount of the crystallization inducing metal contained in the active layer is unnecessarily high, especially when the crystallization inducing metal is Ni and the amount of Ni contained in the active layer is more than 1 E+12/cm2, off-current and threshold voltage Vth become high, and charge mobility resulted from disturbing charge transfer becomes low. As a result, image quality becomes deteriorated, and fault operation occurs in an active matrix flat panel display using the above-mentioned thin film transistor.